To achieve inexpensive small-capacity inverter, only current of two phases of three phases of an inverter is fed back and used for control and shoot-through or output short-circuit generated during operation of the inverter is detected through overcurrent using a resistor for detecting negative voltage (DCN) of DC link voltage or a resistor for detecting positive voltage (DCP) of the DC link voltage to stop the operation of the inverter.
A method using a DCN detection resistor can be implemented through a simple overcurrent detection circuit without an additional power supply since the overcurrent detection circuit has the same potential as the ground of a controller. The method using a DCN detection resistor is widely used because of the above-mentioned advantage. However, when grounding occurs in a phase that does not correspond to a current sensor from among output three phases in a circuit configuration using only two current sensors, the grounding cannot be detected, damaging the inverter.
A DCP detection scheme can detect and prevent all overcurrent situations such as shoot-through, output short-circuit, output grounding, etc. since a current detection resistor is located at DCP of DC link voltage. However, the DCP detection scheme requires an additional tap power of an insulating transformer for driving an IC of a detection circuit because the detection circuit is located at DCP of the DC link voltage. That is, in the conventional DCP overcurrent detection scheme for an inverter, a transformer tap generates power for driving an overcurrent detection circuit, to result in an increase in the volume of the transformer. This increases cost and system size of a small-capacity inverter.